British Insects: Bumblebees and Cuckoo-bees


L. Watson and M. J. Dallwitz

Psithyrus rupestris (Fabricius)

Biology. Solitary insects, parasitic on social bumblebees; the adult populations comprising males and fertile females only; the larvae parasitic in the nests of host Bombus species; hosted by B. lapidarius.

Adult morphology. Adults about 15–23 mm long (females about 22 mm, males about 16 mm). The hair coats of abdomen and thorax all black except for a contrasting abdominal tail. Face at least as wide as long, or wider. The facial hairs of males black; vertex black haired. The facial hairs of females black; vertex black haired. The mandibles of the females obliquely-ended. Antennae of the male with the third segment at least as long as the fifth; with the third segment considerably longer than the fourth. Thorax banded to not banded (all black, or males faintly banded anteriorly and posteriorly with greyish hairs, or females sometimes with a faint anterior pale band); when banded, black posteriorly, with a pale anterior band only (the pale band faint, in a few females), or black across the middle, with pale anterior and posterior bands (in some males); the light thoracic hairs when banded, pale greyish whitish. The outer surface of the hind tibiae of females with no ‘pollen basket’, strongly and uniformly convex, dull and uniformly covered with stout hairs. The hind tibiae of the males having a fringe of short hairs along the outer margin.

The abdomen anteriorly black, narrowly banded before the red tail with grey. Abdomen prettily, conspicuously patterned; with a contrasting tail. The tail orange-red. Abdomen without conspicuous banding between the anterior of the tail and the thorax. Sternite 6 of females without a reflexed spiny process at the tip; without a median keel; with ventro-lateral keels; with large, conspicuous, bulging callosities associated with the ventro-lateral keels; the callosities coalescing posteriorly, forming a prominent ridge visible in dorsal views. Sternite 6 of males without black hair-tufts.

Male genitalia. The sagittae rather straight; with a small hook externally around the middle or somewhat above; apices apically turned outwards, obliquely truncate and minutely hooked externally at the tip, or apically turned slightly outwards and obliquely truncate, not hooked. The ends of the claspers much expanded; pale and soft; conspicuously emarginate and toothed; with the volsella readily visible at their ends (the tip narrowly triangular and incurving, internally fringed).

British representation. Recorded from England, Wales, Mainland Scotland, Hebrides, Orkney, Shetland, Channel Isles, and Ireland. Now widespread in England south of Derbyshire, coastal and eastern inland Wales, and west and southern (especially coastal) Ireland. The adults abroad during May to August (females), or July to August (males).

Illustrations. • Psithyrus rupestris (Black-winged Bumble-bee: B. Ent. 468). • Psithyrus rupestris (detail: B. Ent. 468). • Psithyrus rupestris (dissections: B. Ent. 468). • Psithyrus rupestris: B. Ent. 468, legend+text. • Psithyrus rupestris: B. Ent. 468, text cont.. • P. rupestris: female and male (photo). • Psithyrus rupestris, P. vestalis, P. campestris, P. sylvestris, P. barbutellus: Saunders. • Comparing females of P. campestris and P. rupestris with their hosts (B. pascuorum and B. lapidarius). • Male genital capsules of Bombus and Psithyrus.

To view illustrations with legends giving names in current use, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa, as well as source references and other relevant material.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: Bumblebees and Cuckoobees. Version: 1st January 2012.’.